/*
 * @Author: chen haoxuan
 * @Date: 2021-06-24 21:35:23
 * @LastEditTime: 2021-06-25 22:07:34
 */
#include<iostream>
#include<math.h>
using namespace std;
int main()
{
  void area(int a,int b,int c);
  cout<<"Please enter three sides of this triangle: ";
  float a,b,c;
  cin>>a>>b>>c;
  if(a+b>c && b+c>a && c+a>b)
  {
    area(a,b,c);
  }else{
    cerr<<"Please check your enter!"<<endl;
  }
  system("pause");
  return 0;
}
void area(int a,int b,int c)
{
  float l,area;
  l=(a+b+c)/2;
  area=pow(l*(l-a)*(l-b)*(l-c),0.5);
  cout<<"area: "<<area<<endl;
}